Hashrate...RX480 MSI GAMING X 8Go

Hi

Please i need your help
I have one rx480 gaming x 8gp Gpu
And in claymore on dual mining eth/dcr
I have 31mh/s & 770 mh/s

I have 500 go hdd & 4 go memory at 1600 mhz

But after 2 mn i have less hashrate at 22mh/s & 550 mh/s one or two sequance and became normal after that

My question, is an hdd and low memory can make a trouble in my hashrate or it is another probleme

Thank you for your help