Tensor Tympani Muscle

I used to be able to "rumble" both of them (together or individually) at will. But a while back I had a mastoidectomy in one side, which resulted in the removal of that particular muscle, so now I only have one left to rumble.

One of the drawbacks to not having that muscle is that it is far easier for your ear to "pop" in wind or during air pressure changes, so I find myself often sniffing to re-equalize the pressure.