R6400 Ping spikes

I have a problem with my router or my network card. When I ping to router the ping goes well but it has some spikes I could say every minute. The ping is <=1, but it spikes to 100~200. For 120 packets, there are none lost, but there are two times jumping for 3 packets above 150. There is no other 5 Ghz network around. I am with  DD-WRT v3.0-r31160M (01/18/17). My card is Intel AC7260 and the router is just behind the wall, less than a meter. I've tried different settings but for now the result is the same. Any help is appreciated!