Since the rumbling is in idle car, It should not be the gear oil *
Since you are changing mechanics so much quickly, Every mechanic will tell you their own story. Similar with doctors. Either learn to fix your car your self, Or trust a mechanic.
Tell your mechanic ok change all mounts, But if the problem isnt fixed take them off and return it. You wont pay for it.
Since you have changed clutch from another guy, Everyone will tell you the job isnt done right.
When i purchased this car, The low pressure value was missing, The AC guy kept telling me, Its ok if its not there.
My mechanic kept telling me we cant change direct fan to auto unless you get the low pressure valve.
While AC guy kept telling me it has nothing to do, Fan auto/direct is adjusted from a switch just above the gear.
So everyone has a opinion.