Help... my turntable is alive!

The "heartbeat" sound is still present, but only after the first few minutes and then going away a few minutes after that. I have tried several different records, but still the same effect.

Koestner

Have a look at the arm lift and check that there is clearance between the arm lift and arm when the record is playing. I have had examples where the arm lift is slow to go down ( would explain your results ) and/or the arm lift is not level with the record and varies in height across the record, resulting in contact with the arm whilst playing.. 

moonglum

The OP does not need to buy a new belt. The solution is simply to wash it in warm soapy water then rinse & dry and it will be good as new

You may be correct, moonglum, but you can't know that for sure unless you've actually examined the belt. Even the best belts do stretch over time and require replacement. That's part of why they sell replacement belts. I usually get more than a decade out of mine and you're correct, the soapy water wash often restores it satisfactorily. But all things wear out over time.

Group,
Thanks for all the suggestions. I was playing records last night and again, the noise was gone. I'm now thinking the noise is record specific, or at least some records are a catalyst to the noise occurring. Either way I should point out that the noise is coming from my subwoofers, as I think my main speakers would not produce the noise at any detectable level. So it comes and goes with different records, and I have more work to do in my investigation. Since it doesn't happen on every LP then maybe the problem isn't even with the turntable setup? Lastly I want to say that the noise is very faint and most people would not hear it unless it was pointed out at each occurrence. I'm still trying to get to the bottom of this... will keep you posted.