"Tokay" > writes:

>Over the past few weeks, my Saturn SL2 has been developing an exhaust
>noise.....it's kind of a rattly, poppy kind sound. It only occurs
>under load (up hills, accelerating from a stop, and similar).

Sounds like misfire. I bet one or more of your plugs are shot. Take them out
and have a look. When mine was doing this (occasional pop uphill), about 500
miles later one of the plugs had its insulator touching the electrode and no
spark. My plugs were burning up due to too far advanced timing because I did
not follow the correct procedure to set the timing when I rebuilt my
distributor.