Rattle/Ticking after oil change

I just changed my oil I switched to 5W-30 like the book says, and before I was running 10W-30. Now I have a ticking noise that seems to be on the drivers side, but let me describe it better. Its rythmic, and speeds up with increased RPMs. The most noticable is right when the RPMs are cycling down, but I can also hear it when driving very faintly. Could this be valve train noise from a different oil viscosity? I didn't notice it before the oil change which leads me to believe thats the cause. I don't feel any power loss. Anyone else this?

JTK

98 Cobra - BBK headers & Xpipe, Borla mufflers, custom chip, undriven pullies, 4.10 gears

Hey thanks for the reply. I used a motorcraft filter. The more I listen to it I think its just something loose or rattling behind the engine. I'll jack up the car tonight and take a peek.