I'm new to site bear with me,

I have a 99 Montero decked and bored over a yr. ago

Rear driver side wheel noise when backing up, strange like a relay came on.

And its not a rock...I blend into the trail off roading.

Also,
Anyone know at what temp. does supplementary coolant fan kick on at?

 

Rear wheel noise could be due to parking brake adjustment. Check both sides make sure nothing is loose or hanging up

 

I applied parking brake and hear similar noise, time to pull it apart thanks