Been wondering whether this is an exhaust leak or some kind of special modification done by the previous owner to make it "sound cooler". The sound appears to be coming from the manifold right underneath the distributor area (so closest cylinder to the front of the car). It's been doing this since day 1 when I bought the car in November. It's almost totally unnoticeable when idling but kicks in when under any kind of load. I also experience some hesitation and stuttering every once in awhile when driving so take that into consideration as well. Here's a video clip where you can clearly hear it (apologies for the wind noise). Thanks for the help.