Howling sound at 40mph on 2003 Highlander

[tzimmermn]

I have a 2003 Highlander V-6 AWD (4 wheel drive) with about 25,000 mi. The vehicle is a dream to drive. Recently (last 10,000mi), I have noticed a driveline howl that starts about 35 and gets louder up to about 45. The howl is present with a load on the drive train. It is not present when the drive train is unloaded. I have driven the vehicle under load in a lower gear in the range where I hear the howl. The howl is not present when not in high gear, so I am thinking it may be the front transfer case or the high gear in the transmission. The howl gets less noticeable as you get up to 60 or 70 mph.

Has anyone had any experience with a similar issue? If so, what could it likely be and what might it involve? I have searched your site and did not come across a similar issue.

Thank you in advance.

Terry

[princeofzen]

I have noticed it too. I have a 2001 V6 AWD. I could be way off but my gut tells me it is the acoustics of the engine compartment when the revs hit a certain range and between 35 and 45 mph. Although it would highly unlike Toyota to not have obsessed over something like that...

[tzimmermn]

Thank you for replying. I have no resolution on where it might be coming from and I have not taken to the dealer as of yet to see what they have to say about it. It should be covered under warranty if it is determined to be a problem. I have changed all of the oils in the transfer case and the rear end....no change in the howl. The front transfer case oil was perfectly clean. The rear end was clean, but some gray to black sludge was noted to be on the magnet in the drain plug.

Based upon the symptoms, my past experience tells me it might be that the clearances are set to close on a gear set (location yet to be determined). The other thought that I had on the subject is that possibly the bolts on the drive line may need to be re-torqued and are creating some sort of stress on the rear end or transfer case. This thought may be a long shot, but at this point I am grabbing at straws. I will be changing the transmission oil this weekend. We will see if that has any effect.

If you come with any possibilities as to the source, please let me know. I will do the same.

Terry