After (servicing every vehicle in the fleet), the alarming grinding noises that had been coming from many of the trucks disappeared.

(a) servicing every vehicle in the fleet
(b) servicing all the vehicles in the fleet
(c) every vehicle in the fleet has been serviced
(d) all the vehicles in the fleet had been serviced
(e) servicing all the fleet’s vehicles

What is the answer, and why? Thank you!

A, B, and E are wrong because they suggest that the grinding noises themselves serviced the fleet. That’s not possible—noises can’t be mechanics. (These are cases of modifying phrases gone wrong.)

C is wrong because it uses the present perfect tense when the rest of the sentence is in the past.

So D is correct!