A few problems - need help isolating!

[TimothyD123]

Hi. A friend recently gave me a 97 explorer this past Christmas after having a lot of work done to it including: tune up, CV joint replacement, suspension replacement, various cosmetic fixes, new tires, new brakes.

Recently, Ive started having three problems:

1. When coasting above 45mph, I hear a consistent 'knock' sound every few seconds which feels like is coming from beneath my engine.

2. When backing up, the vehicle will sometimes jerk and make a loud pop noise a single time as though it is having trouble changing gears. This only happens within the first few seconds of backing up regardless of whether I accelerate or allow the vehicle to back up on its own.

3. Sometimes when turning the vehicle on, it makes a loud whirring sound similar to that of a fan. It's almost clanky and it doesnt feel as though its coming from the fan belt or engine. It feels and sounds like it's occurring more in the proximity of behind my gauges in the engine compartment.

Any idea what the cause for these issues may be?

Advice is appreciated. Thanks!

 

[chefduane]

1. Front u-joint maybe? Have you crawled underneath that hand rotated the driveshaft to check for play?
2. See #1 . Bad u-joints can 'clonk' sometimes when putting the car into gear.
3. No clue.

 

[Flash]

#3 AC fan maybe?

Check all your U joints and CV joints.

Is it a 4wd? Are you in 4wd?

 

[deadernie]

#3 sounds like it could be the vacuum powered actuators for the hvac system. Does it only do it when you first start it up?

 

[drdoom]

Transfer case getting ready to go out.