What does clipping sound like?

I think it is mistracking

No kidding. What I said. Ralph was also on the right track.

Question now is, Why? Are we certain we are tracking at the correct VTF?

a 65 watt per channel amplifier was nowhere near enough oomph to drive a pair of small Thiel speakers, but 130/side is just enough to avoid the crackly sound in the low bass that i heard with the weaker amp, when playing organ music.

Sounds like a worn out stylus if it's just with vinyl.

Ok, you didn't provide much information such as how old your components are, how many hours on the tubes, how old is the cartridge, was it set up properly, etc. If this is a new and unchanging occurrence, I agree that mis-tracking is the most probable cause and a great place to start looking. The easiest way is to simply try another source and see if you still get the noise. Once you rule that out, consider tube replacement. Good luck!

From what you describe, it is NOT clipping.

IF it was clipping, it would occur no matter what source, and only at high volumes.

60 wpc/91db/6 0hm is a fairly easy combo unless going for a lot of volume, likely unpleasantly loud before clipping.  

IF only TT, there you go, it's NOT the amp, NOT too little power.

You may want more power, have long thought more power would be nice/better, but don't let this problem go unsolved before moving up in power.

1. prior to alignment issues, check if you are sending too weak or too strong a signal to your preamp's input. what cartridge? what preamp?

2. TT arm/cartridge balance/alignment: how are your skills?