Goaning noise peaks @ 2k rpm: NOT P/S Pump

The goaning noise is similar to power steering pump for american and japanese cars. The noise's sound frequency/vibration can be felt on both fenders from 1000 rpm and peaks at 2000rpm. I clearly "feel" the groaning vibration at the oil lines- return and out- which runs to the oil cooler. I can feel the noise's vibration at the oil cooler as well. The car has 269k mi. Can this be the oil pump? I had the p/s pump out and the noise's vibration is not coming from the a/c compressor either. Thank you.

it can be the oil pump if something was sucked up into that area. but i woundnt think it would cause that much vibration. but if it was the oil pump youll hear it through the whole rpm range. have you done a oil pressure test lately?

Have not done the pressure check.
I'm so puzzled about what can cause this groaning that can be felt on the lines...
I don't feel and hear it after 2k rpm; maybe the phenomenon is being masked by engine noise.
Also, it was intermittent about 3k mi. ago and now I can always count on it to be there whenever the engine is running... like a good friend.
I'll do higher revs while touching the oil lines. Let me get back to you.

do you have an auto or a 5spd?

I'm having the same noise in the same area, and the same vibration in the oil cooler and oil cooler lines. The vibration can not be felt when you touch the block or the oil pan. I suspect there may be a one-way valve in the system somewhere and that said valve may be fluttering at certain rpm, 1000-2000 to be exact. I looked at the parts diagrams at Real OEM, and saw no sigh of any such one-way valve, so I'm going to try changing the oil and putting a different brand of oil filter on and see if that helps. Mine is an '87 325ic, 5-speed, no A/C, No PS, (German-Domestic import).