Dont think you did any damage to the amp, if you had the 2 mid bass drivers in series, thats 6ohms, any amp could handle that in any temp. Now the noise you may hear may be from distortion due to lack of voltage to the amp while under a slightly lower load (now if you had 1.5 ohm that is another story)
Check your grounds make sure they are tight and check you battery connection as well. If you have a voltmeter check the voltage at the battery and then at the amp. If there is a 0.5v or greater difference you need to check your install.
