Q: Car makes noise when starting that goes away when driving. Transmission leak.

Looks like your Toyota 4Runner is actually experiencing two different issues. Let us first start with the noise the 4Runner makes upon startup, that noise that goes away once you start driving. From my experience with working on Toyotas, and owning a 4Runner myself, I would first check the belts and pulleys for wear. The fix could be something as simple as replacing these worn out belts. However, you could also have bearings in the idler or the tensioner pulley starting to fail. This is a commonly overlooked and simple fix. It is important to have a mechanic inspect the noises to avoid spending money on parts you may not need. Your money is better spent elsewhere not on guessing.

As for the transmission leak, an inspection would also be in order to find the source and severity of the leak. If the leak is on the larger side, transmission damage can occur due to lack of fluid and it is important to find this out as early as possible. With anything transmission based, it is always best to have a certified mechanic trace the leak so it can be properly repaired. This is the quickest way to get your 4Runner back on the road for miles to come.