Sewing MAchine Noise

I have a 2000 Isuzu Rodeo with the 4 cyl engine. It has started making a sewing machine noise which gets louder at speeds. The truck does not appear to have anything else wrong with it, no change in oil or gas use. All maint is up to date I have taken it to 3 garages and got threee diffrent answers.
1. broken camshaft
2. idle pully assembly
3. unknown

Any help most appreciated

Mike

this is the famous isuzu tic.

common causes:

low oil
using crappy oil and crappy filters (fram is crappy - sorry)
bad lifters

not changing oil consistently will harm engine parts and the tic will never go away.

change/check your oil... my recommendation: use GTX or Valvoline or Mobil1
and use a $10 filter like K&N or WIX or Mobil1 all the time.

also searching the threads helps too.