Can you post a youtube video, likely it's valve tick but that is typically present at idle as well. You may be hearing timing chain slap or some other vibration.

 

 

Ok I'll admit I'm a bit stumped on this one, it doesn't sound like a valve tick though, it's intermittent once it starts, only loosely increases due to rpm jump. It almost sounds like a relay clicking or some kind of vibration, possibly some kind of exhaust leak only present when the engine is under load and applying torque on the exhaust system.

I think you're going to need a second person to reproduce the problem while you stand at the engine bay and sides of the vehicle to try to locate where exactly the sound is coming from. Unfortunately a mechanics stethoscope isn't going to be very useful over the roar of a 3-4k rpm engine.

 

Does it actually sound like a sort of "sputtering" sound outside the cabin?

 

 

That makes me think it's somewhere in the cabin or inner firewall, cleric might be on to something with the relay answer. Other than that I'm stumped. I've never heard that type of sound on any car, ever.

 

Wow so that sound is CABIN ONLY, that's going to be a fun one to locate and unfortunately I'm not sure what could even make a sound like that. I would start by getting a flashlight and looking around everywhere that you can see under the dash, inside the AC duct vents, etc to see if maybe there's an old paper reciept or something that's fluttering around maybe? You can lay on the floor and press the gas pedal to reproduce the issue and try to get a better idea where EXACTLY the sound is coming from.

 

https://www.myg37.com/forums/tsb-tec...dash-area.html

My car does the same thing.

 

It's loose silicone in the heater core.