amp heats up

I have a 4 channel amp for my speakers. I check the amp after it is on for 15 minutes and I take notice the amp is warm. Its not hot but warm. My other 2 amps dont even get warm. Now on that amp that gets warm, I do have a ground loop problem but I only have it on the rear speakers, so I left the ground alone thinking that a bad ground would cause all 4 channels to have a ground loop problem. So what I did was just run an inline RCA ground loop isolator and it solved the problem. I do have the gains set properly. I have them half way and under. When I feel the top of the amp, its warm, but when I feel the ends of the amp where their are vents, its cool. The amp is around 4 years old. I just want to know if this is normal for amps to get warm. Like I said before, the amp does not get hot to the touch.

Yes it is normal for amplifiers to run warm.  What other 2 amps do you have that are not running warm?

The amp that is running warm is a Earthquake tnt 4 channel amp. The 2 amps that arent running warm are a Kole Audio and a Soundstorm. The soundstorm amp does have a bad ground because I have a ground loop problem but that amp doesnt get warm. The Kole amp is perfectly fine. Is it possible that I have these grounding problems because al 3 amps are grounded to different locations? Well, they are all 3 grounded in the same general location but are about 4 inches from eachother. I also have a battery in my trunk. Could I possibly run another ground wire from the warm amp and run that ground to that battery's negative, that way I have 2 grounds or wont that do anything different? Also, If the Kole amp is perfectly fine that would mean that there is not a high resistance. Could I then just use that grounding location to run the other 2 amps to?

If the amp is not getting so hot you can't touch it, I wouldn't worry about it.  If the other 2 amps are on your subs, it is normal for the sub amp to not run as hot as the High amp.  The highs are always playing, the subs have some dead time between bass notes. 

That makes sense. I was just alittle worried and thought I would ask you professionals. I have heard that Earthquake amps do tend to run warm. The amp doesnt have any vents on the top, only on the ends. So that might be the reason why the top of the amp gets warm. Also, wouldnt the amp go into protection mode or whatever if it got too hot? If so, this amp has never went into that stage. I have all 4 speakers run to each channel so I have the amp running at 4 ohms.

Playing the amp for 30 minutes as in what exactly? Do you mean to listen to the music at the desirable volume for 30 minutes or just have the amp turned on for 30 minutes reguardless if the volume is turned up? The reason I ask is because I hardly EVER go anywhere where I will be listening to my music for 30 minutes. It takes me 15 minutes to get to work. It takes me 20 to get to relatives and so on.

With the amp at the desired listening level.   Check it after the 15 minute ride. 

Well this is what I will do. When I leave my womans house tonight to go home which only takes 5 minutes, I will drive around for 15-20 minutes and then feel it. I will then post the results. Thank you.

Well I drove around for 30 minutes with the system at the desired volume. When I felt the amp, it was just as hot as it was when I drive for 15 minutes. To describe this "hot" it would be the same as if you were to touch someones hair after they had just used the hair-dryer on it. I am able to touch the amp without burning myself. I could touch it for hours if I wanted to. Now the top of the amp is like a big heat sink. Thats the part that I touch. The ends of the amp where the vents are isnt even warm. So I guess the amp is fine then?