Today after getting off the hwy I noticed my van making a loud humming / whining noise. It got louder as I came to a stop and then accelerated again but the sound seemed to stay about the same volume at any other speed. What could this be?

 

Is the noise high pitched, like an electrical sound, if so I would suspect the alternator. On the other hand if it is a growl thane perhaps a wheel bearing.
Auto Zone or Advance will do a free scan on the charging system.

 

I wouldn't say it was high pitched, but it is constant

 

I had a similar issue on my '98 Neon. I put a volt meter on her at rest (20 VDC) and the battery read 12.0 (good battery) I then fired her up and did same test (no accessories on) and she read 14.0 (good alternator), nex t I fired up the AC and lights, the whine came on and I read 12.9 (bad alternator), replaced the alternator and that solved my problem. Again, get a free charging system scan.

 

Could be your PS fluid is low, that makes a constant whining noise when it gets too low. Had that happen once.