I just had the engine replaced 15k ago and the complete front and rear brakes replaces about 5k ago so i know those arent the problem. Only thing i really havent replaced is anything transmission related. Aside from the valve body that crapped out on me 6 months ago. And half the times when im braking it rattles the truck its so sudden of a thud. (Probably unrelated but my front right caliper has locked up and been replaced 3 times now)
My car has 150000 miles.
My car has an automatic transmission.
Check your suspension on your front of the vehicle. It seems that the control arm bushings are worn or damaged and the bolts could be loose causing the suspension to move around when the vehicle is under a load. If you cannot find any parts loose, jack the vehicle up and put it on jack stands. Then use a pry bar and try to move the suspension. If it moves around, look to see where its moving and that will lead you to the correct repair. If you need further assistance with your vehicle making a clunking noise, then seek out a professional, such as one from Your Mechanic, to help you.