Ticking/Rattle Under Light Acceleration

I have a slight ticking/rattle noise under light acceleration. When I get on the on ramp and start accelerating as the rpms go up there is a sweet spot at lower rpm where you can hear it rattle and as the rpms increase it suddenly stops. Its not tied directly to the RPM, but seems to be harmonic or related to a certain frequency. I haven't been able to recreate it in the parking lot. Water pump seems ok, no visible leakage. Hasn't thrown any codes and doesn't sound like pinging/bad gas. Any ideas of where else to look?

 

Figured I would update this. Spent some time under the hood shaking and prodding some of the parts that others have listed as causing a similar issue and I believe I have it isolated to the washer fluid reservoir. When it gets hot it seems to sag enough that it comes in contact with the engine mount/wheel well directly below it. I will be pulling the reservoir and adding some foam to see if that will quiet it down.