On my XS400K, I've been noticing a rear groan that occurs any time there's travel in the suspension. (This bike has the monoshock rear end). I took the seat and tank off, and traced it down to the coil spring and surrounds the shock. The body of the shock does have a plastic cover over it, that I'm guessing is supposed to prevent the spring from rubbing on the shock body. If I press on the top of the spring, the noise goes away, but I can still feel the vibration through my hand.

Anyone have any tricks on how to get this to stop?

I put coil spring over shocks on the rear of my minivan, and they squeak a bit when the spring rubs on the plastic covers. I use a heavy duty silicone spray and hose down the whole spring/ shock assembly and it works for about 6 weeks (or until it rains for a few days). I would guess this would for the monoshock assembly on the bike too. My '82 400 Maxim hasn't done this yet.

That's a good thought.... I'll have to run out and get a can. I tried motor oil on the coils earlier today, but it didn't hang on long enough. Plus it makes a bit of a mess.

I don't think the water should be too much of a problem on this, as the spring is nicely tucked up into the bike and appears to stay dry.

On my XS400K, I've been noticing a rear groan that occurs any time there's travel in the suspension.

Anyone have any tricks on how to get this to stop?

yep, stop the wife riding pillion,works every time for me