Is it a standard or automatic? I had a 1995 Nissan hardbody 5 speed that started making a tapping noise like that, and when I pressed the clutch in the noise went away.
Took it to the transmission shop and they said it would be $1400 to fix it. I dont know what it was, but I only paid $500 for the truck so I sold it to a mexican like it was.
May look into that..
