As I learned before, the peak voltage value of two combined sinusoidal signals is the sum of the two amplitudes, for example, \$0.6\sin(ax) + 0.8 \cos(bx)\$ can be \$+1.4\$V or \$-1.4\$V. Would it be the case for the noise?
For example, if now the output noise signal is \$1\$Vpp and my desired signal is \$1\$V at \$1\$kHz. Would the peak value of output become \$+2\$V or \$-2\$V?
One more question: If the answer of the above question is yes, would an amplifier which limits its output to the range \$\pm1.5\$V saturate at that time?
Most of the noise that occurs in electronic instruments and in environment is additive noise, so yes, if a noise is of same amplitude as signal, both will add to generate higher voltage signal and yes it can saturate the output level. Usually, at any instant of time the value of output signal is equal to signal value plus noise value at that instant of time. But with the use of current op-amps which are compensated with higher input impedance, lower output impedance, rail to rail, higher PSRR, CMRR etc. u can get lower noise generated within amplification device. The other noise u may find is phase noise where phase of signal fluctuates to create jitter. U can go through noises from here http://en.wikipedia.org/wiki/Noise_%28signal_processing%29