The main point of an aerial amplifier (sometimes referred to as a signal booster) is to amplify the whole signal (this means all the frequencies within the range). Of course this can amplify any interference too. So, you need to make sure you have a good signal to begin with. Check your aerial is correctly aligned and any masthead amplifier (if you have one is working properly).
A common cause of interference is the coaxial cable from the aerial to your TV. The cables can fill with water (especially old cables), and sometime long cables (especially if not well shielded) can act as giant aerials picking up all kinds of interference. Adding an amplifier can sometimes make things worse. One way improve things is to rewire with new good quality shielded cable and/or to locate the amplifier as close to the aerial as possible so you are not amplifying the interference. This is why aerial amplifiers are often found in lofts. Putting an amplifier next to the TV with the poor signal will only amplify the poor signal.