Vibration and looseness - Solved

[HairTooLongToo]

Sharing my resolution for a vibration issue I was having.

Symptoms: vibration like how it feels when a wheel is out of balance or it's flatspotted from sitting for too long. Was only noticeable from 50mph and faster. On the highway in addition to feeling it through the seat and armrest, it also made a very noticeable thrum. There was also a clunky feeling looseness to the steering that was very felt when turning up onto driveways.

Solution (I think): found that all the bolts for the under-engine reinforcement plate were quite easy to undo, so snugged those up to 56nm per spec but didn't do the final 90*. My car was also missing the center exhaust brace, and I replaced it at the same time. I wasn't doing this to chase the issue, but it so happened that I noticed the car wasn't vibrating anymore afterwards.

So hope this helps someone. The reinforcement plate and exhaust brace gets taken off for lots of reasons, so worth it to check out.