a couple days ago my cousin and i replaced all four brake rotors [got drilled/slotted from GREDDY2GREDDY] and recently have had a weird noise when i go into reverse [SOMETIMES].

situation 1 - i drove to CSULA which is 30 mi away from my house. when i was going back home though [after warming up car] i went into reverse and it made a whale like noise, and i thought i might have ran over something. i looked around and nothing was there. i put it into neutral and tried to put it in reverse again, but i could NOT replicate it again.... so i thought nothing of it.

situation 2. i was backing up into my driveway and its about a 20 percent incline. i go into reverse and the same whale like noise happens again! at this point i know it had to be something. so i kept trying to replicate it, so i put it in neutral and hit reverse again and again, but could not replicate.

these two situations happened in the last couple hours.
another thing to note, when we were changing the rotors, the rear pads were kind of thin, but i find it odd that it did not do that before with the OEM rotors.

any ideas?

 

I'm going to assume you put your parking brake all the way down and made sure it was.

Since it is only happening after you put on your rotors, it's almost certainly that. Is is directed at any one wheel you can pinpoint? more than one wheel? Have you visually inspected the rotors and pads, making sure they are even?

My bet is that the pad is sticking or something like that at least on one wheel, or something is shifting just as you reverse, which is why it only happens once in a while.
Of course.... I have no idea what it would be besides uneven pad/rotor or you possibly put the rotors on incorrectly, not enough axle grease? Did you wipe a bunch off by any chance?

 

well i tried it again, and nothing. but all i did was replace the rotors, NOT the pads. planning on getting Hawk rear pads
but i guess that makes sense, since i did not put any grease that wasnt already on the pad.

 

yea, your probably right, it is the pads against the rotors. i didnt scuff the rotors before installation, because i got the rotors from GREDDY2GREDDY, and he said they were used for 100mi. in the last three days i have driven 2x that amount since i commute at LEAST 60mi a day [highway]. but the groaning noise did not start till today
i would have got the rotors cut, but i really didnt think it was necessary [at the time] .

 

do some hard braking to scuff the rotors in.

 

thank Charles!