98 'lude, 77,800 miles, no modifications.

I'm hearing a low growling noise when revving at around 1000 - 1500 rpms. It's coming from near the block (maybe inside?) / exhaust manifold / alternator. It's definitely different than the sound of the cams ticking. The car idles slightly louder and i believe it's related to this problem. Any major cause for concern?

I have been getting Primary H02 Sensor Error Code 61 (slow 02 response), perhaps this may be an exhaust leak/deterioration that's causing the noise. Anyone have any ideas?

Thanks.

 

it's time for a valve adjustment.