Low RPM Vibration Resonance

[f22beaver]

2008 JKU with a 3.8L and 42RLE.

I've read this from a couple different people but either people are terrible at updating their posts or they just never actually fix this.

At around 700-900 RPM's I just get a pretty steady vibration throughout the vehicle, just like a low/deep vibe. It's more pronounced at temperature than at cold start. This is not wheel imbalance as I'm stationary but it also can happen if the trans happens to shift into a gear that gets left at that RPM. I suspect it's just an engine resonance, but has anyone ever fixed this? Engine/trans mounts are too expensive to just throw parts at it. And my trans mount was recently off, no cracked/separated rubber.

I've seen once or twice where it's the torque converter. Definitely NOT throwing parts at that.

Some people speculate plugs, which.....maybe? They're not that expensive and I don't know their history as it's a new to me Jeep so I may just change them as a part of preventative maintenance.
Update: My local AutoZone had the Bosch Platinum 6720's for $3. Absolute steal!! And an easy 15 minute job so I just went ahead and changed them. Maybe slightly better? But definitely not gone.

I'm not too worried about it. I classify it as one of those mild annoyances of driving a 14 year old vehicle, but figured I'd ask.

Thanks!

 

[Anybodyhome]

I won't tell you what to spend/not spend money on, but I would offer these possibilities to inspect on your own:
Motor mounts, u-joints, bushings, shock rubbers, etc.
Although they may be a pain or too expensive to replace, whether or not the vehicle is in gear matters not. If there's engine vibration, it's going to resonate exponentially if there are worn/bad/missing bushings, etc.

 

[Dirty Dog]

Vibrations pretty much always mean something is moving in ways it's not supposed to. Something has broken loose. Or something is out of balance. Or something is aligned wrong. Broken loose is the easiest to spot. Poor alignment is much harder. Out of balance is nearly impossible to tell without taking the part off and spinning it. Because you can't really watch your driveshaft (for example) spin while you drive down the highway.