This is going to sound ridiculous but immediately after changing my transmission mount I began experiencing a concerning rumbling/vibration feeling along with what can be described as a humming type sound. The rumbling feels like going down a gravel road and is present even in neutral. The sound begins only while accelerating from a dead stop and eventually goes away but the rumbling feeling remains. The rumbling feel is present through the entire rev range in neutral but is less noticeable after the 3500rpm mark is hit. The ECM is not throwing any codes either. I have verified the motor mounts are solid as well. I am strongly suspecting the torque converter but I want to see if anyone has any ideas before I spend time pulling the engine out in this crazy heat.

I have a 1998 Montero sport LS, RWD, 3.0L.


EDIT: I checked the new transmission mount and it seems solid, I believe this has been an issue for some time but the old mount was softer/sat lower so I'm thinking I just never noticed it before.

 

I was driving in town today and noticed a new symptom, at idle I felt a slight surging, I glanced down at the dial and noticed it fluctuating up and down about 75~100 rpm, it has never done this before in the 8 years I've owned it. I am now questioning the torque converter theory but this is still a common symptom as far as my research tells me.

 

Y'all I feel retarded. This new transmission mount is made of a form of synthetic rubber. It's stiffer than both the OEM mount and the worn out aftermarket I had on there before. I am just feeling the normal vibrations of the engine and drivetrain. The surging is something else entirely and likely to be the IAC on it's way out. I hope somebody with this same exact issue sees this and it helps them not spend a ton of money on something that didn't need fixing. As for the humming noise, who knows, it's probably nothing.