Possibly the wheel bearings

I thunk that there was non.

Yep .

No, "thunk" is not the past participle of "think". It is not even a word. The correct form would be, "Who would have thought it?" Sometimes "Who'd have thunk it" is used for humorous effect, with the understanding that the speaker knows it is not correct English.

"Thunk" is not proper English at all. It is used either humorously or ignorantly. The word is "thought."

Thunk is a sound made by a falling or thrown object when it hits something, similar to thud.

A thunk in computer science or computer programming refers to a hidden activity occurring when passing possibly incompatible parameters to a subroutine.