At Idle when A/C on car rumbles/shakes

[searcherrr]

At Idle when A/C on car rumbles/shakes
143k miles and no known a/c service ever.
Idle remains at 750 rpms very steady when A/C is OFF. IAC is in good shape.
Idle remains at 900 rpms when A/C on.

What's the usual cause of this that ya'll have found? Low on freon? A/C flush needed?

If I can get away with just a flush I'd of course rather that than replacing the compressor, but it would be nice if someone said they'd experienced this and what fixed it.

Also, I think I already know the answer to this, but based on what someone else told me I ask: Does not flushing the a/c system over time lead to a bad a/c clutch? and why?

I recently tried to replace the a/c clutch to no avail because in the past its made the metal-to-metal sound very badly, but its very hit and miss and more miss on when it does it. Its like it would catch on a certain spot and only do it then.

Now before ya'll flame me for obvious reasons, since I couldn't get the clutch off no matter what I did (jaw pullers and everything; bent up the pulley) I cleaned and oiled the clutch quite thoroughly hoping I'd get some more use out of it. It kicks on now hardly without a sound being made ... very smooth at kick on and the air has ALWAYS been cold and still is satisfactory.

After kick-on though the car just rumbles/shakes when at idle 900rpms. Could the belt be too tight? I didn't know how tight I should make it when I had put it back on so its good'n tight and idle holds amazingly steady at 750rpms when A/C is off and steady at 900 when its on. I guess it could still be the clutch and is just less noticeable since I cleaned/oiled it?

EDIT: When driving I do not notice the shake, rumble, or performance degradation. However I did recently switch from IK24 plugs to IK20's cause the IK24s were too cold for my NA setup with the biggest mods being an Ebay pipe and MSD 8.5mms. I was troubleshooting off the line pickup issues which it still seems like my mom's 2001 3.0L Maxima has better off the line pickup than my 3000, but now I'm just wondering if since I haven't driven it in 3 years that its just the 1st and 2nd gearing of the ATX I'm noticing.