General Maintenance & Repairs - Odd problem...

Well normally I drive the car in drive and after a while i start to hear a loud tapping sound after 15-20 minutes of normal driving(that increases and decreases in sequence w/ rpms) so im thinking lifter problem. Local buddy is a mechanic and we took it out today to see if we could diagnose the problem... Now I recently just bought the car and its a rebuilt a4 w/ 342's but when its in drive it sounds like the rpms are awful high at regular cruising speeds. So needless to say we threw the car in overdrive and took it out for a good cruise and no sound whatsoever...Very odd, were thinking maybe the rpms in drive are to much for the top end under normal driving. Anyone ever hear of anything like this...all the cars info. is in sig...thx guys.

cracked flexplate?

3:42'S in drive will tack @ a higher RPM than overdrive but the ticking noise in D and not OD is strange.Is it still their if you ride around in drive again ?

Didnt really drive it that much in drive....

Possibly an oiling issue getting to said lifters at higher RPM. Would make sense b/c you said you don't hear it in OD, which would be lower RPM's. Hoping not, but at worst case, it could be a failing oil pump, but most likely only if this problem is at high RPMs.