Alright, i've got a 2001 burb with just over 100k miles and something happened this past weekend while driving home form a friends house. Its been shifting in and out of park/rev/drive kinda hard but nothing too tough lately so i didnt think anything of it. Once i got home trying to park, there was a lound clanking sound under the body...sounds like drivetrain/tranny area. I parked it and let it sit over night....too dark and too late to work. The next morning i went out and she cranked fine, moved smoothly in reverse not a sound at all and then BAM!, i put it in drive and this loud clanking sound begins. After a day of troubleshooting i've noticed that it doesnt happen when the brake is engaged, but the second i let off the brake it begins to bang...any ideas?

Thanks in advance

 

Yeah something is broke. Just kidding. BUt it does not sound good. Hopefully someone with more expertise will help you.

 

U-Joint maybe??