Does anyone know how I can check the grounding for my system?

Actually you are NEVER supposed to ground all components from the same spot. Grounds should be less than 18 inches long, and always either the same guage or a larger guage than your power wire. As for checking them, get a digital ohm-meter and set it to the thousandths setting(.000). Put one lead on a clean bare piece of metal, then touch the other lead to the ground(s) of your components(headunit, eq, amps), if you get a reading other than .000, you have a bad ground. Disconnect the leads, clean terminals and grounding locations, clean screws and bolts, and re connect any butt connectors making very sure they are tight. You may also apply a small amount of di-electric grease into new butt connectors to ensure positive contact and prevent any corrosion that may occur although unlikely!

not really that many steps

clean off a section of paint from part of the chassis of the car and drill a hole

firmly bolt a thick cable to the chassis then connect to the negative of the amp

for a "belt and braces" approach, bolt a second cable to the chassis and bolt it to the casing of your amp

theoretically all ground connections should be made from one point to all of your system [it's called "star earthing" but its very impractical and you will get away without this in 99% of cases]

that's pretty much it - if you want to make sure of the chassis ground, run a heavy duty cable from the negative of the battery to the same earthing bolt on your chassis as described earlier

i doubt you will have an earthing problem after that

Good luck

Andy