Initial decay increasing with sampling rate

Hello everyone,

I'm experiencing an initial decay in my signal that increases with increasing sampling rates. I've included my acquisition code and examples of acquiring the signal with 1 kHZ and 10 kHz sampling rates.

I'm acquiring three physical channels using a USB-6003 DAQ board. By the time I run my code, the amplifier is already working and sending data to another computer through a RS232 cable.

I'd love to know what could be causing this, since the code is very simple. Could it be a hardware issue?

Thanks in advance,

Lucas