adding noise of frequency 750 Hz to a signal which is sampled 60000 times in 60 secs.

I have a pressure signal data with 60000 samples of data captured in 60 secs. I want to add a noise of 750 Hz to this signal. When I add the 750 Hz noise using noise generator block in simulink, I am observing that the number of samples in the output signal is reduced to around 45000. If the noise has a frequency same as the signal data i.e 1000Hz, then I am not facing this problem. Is there a solution to this problem.