I have a 2008 Hummer H2 with a 6.2 l GM engine which deve...


I have a 2008 Hummer H2 with a 6.2 l GM engine which developes a hissing noise when accelerating and a flapping noise only when is accelerating and driving uphill. What could be the cause of this? Can you maybe pinpoint to some ex...

I have a 2008 Hummer H2 with a 6.2 l GM engine which developes a hissing noise when accelerating and a flapping noise only when is accelerating and driving uphill. What could be the cause of this? Can you maybe pinpoint to some exact component on base of your experience. Thank you! Best regards. Drago Mechanic's Assistant: Where exactly do you think the noise is coming from? And how long has this been going on? I think it is comming from the right side of the engine bay. It is going on for apprx. 5.000 km (3.000 miles) Mechanic's Assistant: Are you fixing your H2 yourself? What have you tried so far? I am based in Europe. It was fixed by some mechanics, but the basic stuff but the basic stuff I always did always by myself. Recently the right valve cover gasket was leaking a bit and I changed it, but the mentioned noises did exist before that. I also changed the small PCV valve on the left valve cover and changed both PCV tubes and also cleaned the air intake (snorkel) as there was a modest track of engine oil in it. but the basic stuff I did always by myself. Recently the right valve cover gasket was leaking a bit and I changed it, but the mentioned noises did exist before that. I also changed the small PCV valve on the left valve cover and changed both PCV tubes and also cleaned the air intake (snorkel) as there was a modest track of engine oil in it. Now I am also changing the left valve cover gasket. 2.500 miles back I changed also the engine oil and oil filter (all imported by me from USA - AC DELCO UPF48R filter and Valvoline high milage engine oil with Dexos 1 specification) Mechanic's Assistant: Anything else you want the Mechanic to know before I connect you? The axhaust manifold bolts are all in tackt. There are no codes popping up. That is for now. Thanks

Automotive Expert
Welcome to JustAnswer Drago. Thank you for contacting us for assistance with your vehicle. I'm Pete. I will be happy to assist you with your question. Was anything done to your vehicle that may have caused this issue before the noise started?

Hi, The vehicle was serviced regularely mostly by me. I use top materials and keep to the scadules. I owe it for last 90.000 miles. Now there are 126.000 miles on it. The noises just developed 3.000 miles back. The hissing noise by acceleration / reving is like suction noise, but I can not fine any airleak.
Automotive Expert
Hello. Nice to hear from you today! I'm sorry to hear you are having this problem. I know this can be frustrating. Is there a lack of power at all with this issue?

It might be a slight (not realy much) lack of power when accelerating uphill. That would be also when the flopping voice would appear.
Automotive Expert
Thank you for your reply and that information as this does help me better understand the situation. Please give me one moment to type out some info for you. I’ll be right back! Thank you for holding Drago! The hissing and flapping noise that is occurring can be caused by a broken internal exhaust component. I have seen the catalytic converters come apart internally to where they will cause a hissing noise to occur as well as the flapping noise and an issue in some cases with a loss of power when under load like driving up a hill. I recommend having the exhaust checked over for any visual issues needing to be repaired. If no visual issues are found then the exhaust will need a back pressure test performed by a shop or dealer. They will usually charge around $100 for this test. The exhaust also needs to be tapped on to see if anything is rattling. The drive belt should be checked for any pulleys out of alignment as well as belt issues. I also recommend having the air intake inspected for any restrictions or loose components. All of these will cause this issue and need to be checked into to identify the fault.

Ok. I alredy checked (and changed both belts, tensioners and puleys) the drive belt for any pulleys out of alignment as well as belt issues and I have inspected also the air intake for any restrictions or loose components. Everithing there is ok.Exhaust gaskets and bolts also seek ok.I will one more time make the visual check of the whole exhaust system as you sugested.Can you please tell me how this back pressure test performed. Is it with the compressed air trough the exhaust pipe and than detacting an airleak with the help of some sope mixture (boubbling) or is it there more sufisticated aproach needed. I am asking this, because I am based in Europe and here the technicians do not have a real experience with "big american vehicles".Can I damage something, if I blow air with the aircompressor into the exhaust tailpipe to build preasure in the axhaust to find leaks?I am quite certain, that he hissing and flapping moise is comming (at least I can hear it while I am driving) from tje right side of the engine compartement.
Automotive Expert
The exhaust back pressure test is performed with a pressure gauge that threads into the pre catalytic converter oxygen sensor port. Then the engine is started and ran from idle to wide-open throttle briefly to see if the backpressure exceeds 1.5 psi at any time. If the backpressure exceeds 1.5 psi at any time then that does indicate a back pressure issue due to a damaged or restricted exhaust component. You can blow air in the exhaust if you like but it may not show the issue, unfortunately.

Thank you Pete. I wil get the exhaust checked/tested.I am just now in the midle of changing the power steering radiator. Can you maybe tel me, if I need to drain out the whole power steering system first as I somehow can not loose the two nuts that atache the radiator to the pipes at the front of the vehicle. Is there so much presure in it or would the corosion be the cause? How is it the best to do it? Thank you!
Automotive Expert
Your welcome! Unfortunately, since your last question is in regards \*\*\*\*\* \*\*\*\*\* new issue, according to website policy it has to be opened up as a new question. I wish I had some better news to tell you on that. You can request me to help you with that question if you would like by using the link below. [https://www.justanswer.com/profile.aspx?PF=14928985&SRD=true&rpt=21004](//www.justanswer.com/profile.aspx?PF=14928985&SRD=true&rpt=21004)
Automotive Expert
Glad I could be of some help! I hope everything works out well for you! If there are any additional questions on this issue that should arise, please feel free to reply and ask! Thank you for choosing Just Answer for your questions. Have a great day!

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