Try out the Tremelo plugin.
You can change the Phase to make it pan around the stereo field, and by tweaking the Symmetry and Smoothing you can get different fade in effects.
The other alternative it to use automation and draw in the pan and volume fades.
Gary's suggestions are spot on.
Another option is to set up a side chain via a compressor on the guitar track which responds to a source (e.g. kick) on another track. You can get a pumping sound that way...