Any thoughts on why I would be getting an intermittent driveline shake? Recently on the way back from Atlanta, which is about 2 hours away, my 2016 BMW X5m began to have an extremely noticeable shake that I could feel throughout the vehicle. It felt like a bad universal joint to me. It would come and go at random but was particularly apparent when accelerating and would mostly go away within a few seconds of letting off the throttle and coasting. My first assumption was that the front prop shaft was out of balance or had failed since it felt like a universal joint and from what I understand they are a common failure point.
After replacing front prop shaft I had no more issues the last couple weeks, including another trip to Atlanta, until today. Same symptom shaking while on throttle (intermittently) and then mostly goes away or completely goes away when coasting. My second assumption was rear drive shaft but I don’t think that’s it either after inspecting. See video below:
I’ve “shook” all the suspension components, transfer box, etc. it all feels tight and secure. Wheels are on tight with lug bolts properly torqued. Wheels aren’t shaking when freewheeling nor is steering wheel shaking so it isn’t an out of balance tire. Also an out of balance tire, out of round rim, etc. wouldn't come and go, it would always be an issue.
A few other pieces of information. I just changed all the driveline fluids about 1,000-1,500 miles ago. That included front diff, t-case, tranny and all 3 chambers in rear diff. T-case was recalibrated without issue and appears to be working properly. Prior to renewing the t-case fluid I had the "pulling a trailer" feeling that you get when the t-case fluid is shot.
Observations during the fluid change:
1. Tranny oil looked great. Renewed filter at same time. No issues with shifting.
2. T-case fluid was dirty but not abnormal, calibrated and no issues.
3. Front diff fluid looked horrendous, like soupy mud. The previous owner supposedly renewed the front diff, which I did verify with the indy shop, but apparently they renewed it with a used one and didn't change the oil??
4. Rear diff oil looked normal in center chamber and right chamber.
Left chamber was almost empty.
Filled up front and rear (center) diff with Liquimoly. T-case and rear left and right diff chambers received the correct BMW brand oil. Tranny got ZF brand fluid.
I’m thinking that it may be an engine mount going bad, loose or something along those lines. Other thoughts are a CV joint going bad but they all looked good when I was running the vehicle on jack stands. The fact that the shake is intermittent and only happens while "on throttle" leads me to believe it's a driveline component failure but the intermittent nature of the shake it is really puzzling. It would seem to me that if the front or rear diff, tranny, transfer case, etc. were failing that they would be failing all the time, not just here and there. Any ideas?