Delica Canada | Mitsubishi Van Club

If the front axles are locked or unlocked, 2H or 4H, there is no usual sound from the front end.

If by some odd chance the ring or pinion gear is worn or backlash is not set properly, then you'd hear a metallic howling sound on acceleration, NOT deceleration.

Sounds on deceleration would be linked to brakes or cv shafts or suspension components.

Have a mechanic look at it.

The front end is almost identical to Toyota 4runners.

Also the system relies on a vacuum to operate an actuator rod on the front axle.If there is a leak in the system or the actuator rod is sticking it may not be engaging fully pointing to flashing lights. You can test this out by using a vacuum pump to check or shifting between 2h and 4h on a slick surface and see if only the back wheels spin.
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It's better than a poke in the eye with a sharp stick!

I already had a mechanic look at it (Butch @CVI), he couldn't see any problems. It makes the noise intermittently. From what I gather there is a vacuum-operated freewheel clutch that disconnects the right wheel from the diff. The left wheel continues to turn the front driveshaft. Whether that clutch could cause the whirring noise, I dunno. Could be a CV I guess. Perhaps a wheel bearing. Definitely not the sort of noise brakes can make.

When you get the noise...

are your front 4WD lights flashing or on constant ?

Over in the UK we have got very used to super select problems... most are fixed easy just with use !

sometimes you need a new vacume solenoid.

You must not drive about with the front super select lights flashing... if this happens go back to 4WD....

we have had members blow diffs doing this for a prolonged time....