Sounds lightly like the vowels are typing but not sure

Valves may need higher octane, or injector(s) may need cleaning. Tapping should be constant if it was a valve issue tho. Sounds like it's "engine knock" due to lack of good fuel supply. Try running a can of fuel cleaner thru a tank and see if it changes. Mite try going to higher octane fuel and see if it remedies the problem. Hope this helps.