Newbie needs help

I just bought a certified Toyota ,but it has been over 1,000 miles so I can't take it back under warranty. I notice a knocking noise under the bed when I am coasting and have no gas applied and brakes not appplied. The knocking stops when I apply brakes for the most part. It is pretty loud enough to where it doesn't sound right.

it is a 2001 2 wd automatic 4 cylinder extended cab. Anybody have some ideals on what I could check.

Thanks for your help,
Ron

how many miles?
if you haven't isolated the noise, may check the two-piece driveshaft, and/or the carrier bearing for the propshaft.
could be something as simple as prior owner's once had a flat, and didn't put the spare all the way up, allowing it to slop around.

hope this helps,
chris
nrt racing