05 90 2 stroke tnt makes a popping sound

I have an 05 90 2 stroke and the trim n tilt unit makes a popping sound. When the boat is under power (at least 1500 RPM) the unit sometimes pops when I try to tilt the motor up. Tilting back down under load it really makes a popping sound.

Any ideas?

[boats.net]

Could be the bushings sticking on tilt tube where motor pivots or could be the short trim rams dragging on motor bracket. Put grease on ends of short trim rams where they come in contact with motor housing, grease fittings on tilt tube.