For 2 years my eardrum has thumped when I lightly touch my ear. Mri shows nothing, ENT stumped?

The thump is a stump. The facial nerve runs in a bony canal next to but not on the ear drum. The stapedius attaches to the stapes not on the ear drum. I'm not sure why you have that sensation... We are all unique. .. Normal mri. No worries.
Facial Nerve. A small branch of the facial nerve runs along the eardrum. A small muscle the stapedius also runs along the eardrum and is connected to the facial nerve. A problem with these structures may give you a problem with hearing a thump.
Eustacian tube. Sounds like pressure changes inside ear. Try to drink a lot more water, chew gum frequently, take Mucinex (guaifenesin) plain over the counter, and use prescription steroid nasal spray for 2 weeks. If it doesn't improve, may need to see neurologist.