Buy High Pass Filter or KAB RF1?

Just build your own and experiment.  $25 filter is just probably a resister and a capacitor.

Thanks Brandon I’ll stay in touch! I just saw your first post. This is crazy isn’t it?

im now thinking about buying the out board pre amp first so I can get the table away from the speakers and see if it’s a feedback issue. 
I have also heard that you can buy a test record that will help to identify the problem but it’s like $50.

i also saw in another similar thread that if you turn on the turntable but don’t play the record and then crank the volume way up that if the speakers pump it’s a feedback problem. 
Finally somebody told me if it’s a feedback problem that a filter won’t work but I thought that “rumble” = “feedback” problem.

i am convinced a simple passive filter will hurt sound since the designer of one mentioned in this thread told me it technically does. He said whether you hear it or not is another story. I have also read that while an active filter may not degrade sound it may throw the bass out of phase. 
I thought I was simply just going to buy a record player and spin records a couple months ago. Lol 

Do the woofers flop with the sound turned down?

What program material? I have some classical recordings where the HVAC is blowing on an unscreened mic. The sub worked so hard it shut down.

If you can see your woofer’s flopping, it is likely below ≈10Hz which is very low for feedback.

It’s over 30 years since I had a turntable, the last ones had disc clamps which do wonders. The TT, HA & Pre were in a separate room... ZERO feedback at any playback level.

’Rumble’ filters on consoles and pre-amps are often quite high ≈40Hz.

The db systems HP is just a ≈140nF cap. Actual frequency will vary if phono impedance is not 45k. It will only ½ the excursion @ 12Hz. An adjustable multipole filter [4th order L-R HP] to the sub and bass driver amp is preferred.

The KAB RF1 is mono below 140Hz. Not all LPs are mono below that frequency.

@craigert No problem!  In my case I don't think it's a feedback problem, as I recorded (without the speakers on at all) to a digital recorder and played it back and the woofers still pumped. 

I feel you on the passive filter...but for $25 I think it's worth a shot. I ordered them on Friday so got 15% off, which offset the exchange rate a bit.  Still cost me $20 in shipping though. Insanity.

My woofers DON’T flop with the volume turned down. 
It started out of nowhere on my AJA album Black Cow. Something wasn’t right so I switched to Led Zeppelin II and it was rumbling on that too!