My rear speakers are making a cranking sound wen I push the sound too laud so a Thoth on buying a pair of more powerful speakers (200W / 100RMS 3 Way), but do not know if the car radio has sufficient power for the speakers or if the problem will persist ... My car head unit is a Blaukpukt 4x45w... Note that i do not have an amplifier and do not intend to install one ...
There isn't a head unit available on the market that will "properly" run an aftermarket speaker. They're ususually 25 RMS per channel which is the numbers you should look at when playing with audio. Pay no attention to dynamic power. Anytime you buy an aftermarket speaker its usually best for both sound quality and the speakers life expectancy if you run it off an appropriate sized amplifier. From what I know the RMS rating on amplifiers is measured differently than that of a speaker. Speakers are measured buy their peaks. Try running a 2x60rms amp to them if you can afford it.