How can I diagnose what is interfering with my Wifi signal? I have a mysterious  process on my Macbook pro which I can't isolate which comes around every 5 seconds and interferes with my connectivity.

My ping history looks like this:

    4 bytes from 216.58.194.174: icmp_seq=12996 ttl=53 time=93.144 ms
64 bytes from 216.58.194.174: icmp_seq=12997 ttl=53 time=22.797 ms
64 bytes from 216.58.194.174: icmp_seq=12998 ttl=53 time=23.122 ms
64 bytes from 216.58.194.174: icmp_seq=12999 ttl=53 time=23.674 ms
64 bytes from 216.58.194.174: icmp_seq=13000 ttl=53 time=23.827 ms
64 bytes from 216.58.194.174: icmp_seq=13001 ttl=53 time=21.925 ms
64 bytes from 216.58.194.174: icmp_seq=13002 ttl=53 time=22.654 ms
64 bytes from 216.58.194.174: icmp_seq=13003 ttl=53 time=754.820 ms
64 bytes from 216.58.194.174: icmp_seq=13004 ttl=53 time=1448.052 ms
64 bytes from 216.58.194.174: icmp_seq=13005 ttl=53 time=1144.956 ms
64 bytes from 216.58.194.174: icmp_seq=13006 ttl=53 time=165.125 ms
64 bytes from 216.58.194.174: icmp_seq=13007 ttl=53 time=22.109 ms
64 bytes from 216.58.194.174: icmp_seq=13008 ttl=53 time=22.513 ms
64 bytes from 216.58.194.174: icmp_seq=13009 ttl=53 time=23.716 ms
64 bytes from 216.58.194.174: icmp_seq=13010 ttl=53 time=22.804 ms
64 bytes from 216.58.194.174: icmp_seq=13011 ttl=53 time=22.349 ms
64 bytes from 216.58.194.174: icmp_seq=13012 ttl=53 time=21.941 ms
Request timeout for icmp_seq 13014
64 bytes from 216.58.194.174: icmp_seq=13014 ttl=53 time=1200.319 ms
64 bytes from 216.58.194.174: icmp_seq=13015 ttl=53 time=933.177 ms
64 bytes from 216.58.194.174: icmp_seq=13016 ttl=53 time=206.759 ms
64 bytes from 216.58.194.174: icmp_seq=13017 ttl=53 time=23.897 ms
64 bytes from 216.58.194.174: icmp_seq=13018 ttl=53 time=22.536 ms
64 bytes from 216.58.194.174: icmp_seq=13019 ttl=53 time=21.755 ms


I can tell that this is local to my machine (and not the network) because these results don't change when I switch networks and other machines on those networks don't show the same intermittent stagnation.

I have closed every application that I can including the obvious background ones (Dropbox, Google Drive, etc.) but the problem persists.

At this point I'm at a loss as to how to pinpoint what service or process is doing this. I'm hoping someone has some remedy or third party tool I can use to isolate the culprit and shut it down.
A request timeout on ICMP (ping) going from your Mac to your your network device simply means that the device, not your Mac failed to respond to the ping request in a given amount of time.  There is a good explanation of that here.

This can happen for any number of reasons; network congestion, device load, wifi signal interference, power loss, etc.  Most importantly, it has absolutely nothing to do with services that are running on your Mac.  

Based on the address you used, it looks like you are pinging google.com.  This means that between your Mac and Google's servers there are a number of "hops" that your packet must go through.  Your Mac to your Wifi is one hop.  Wifi to your router/modem is another hop.  Modem to your providers gateway is another hop and so on until you get to Google.

To see how your hops are performing, issue the command traceroute google.com and it will output something similar to the following:

    1  pfsense (192.168.10.1)  0.401 ms  0.176 ms  0.223 ms
     2  96.120.36.197 (96.120.36.197)  23.503 ms  8.269 ms  8.470 ms
     3  xe-1-3-0-0-sur02.miramar.fl.pompano.comcast.net (68.85.82.157)  9.371 ms  8.740 ms  8.517 ms
     4  xe-11-2-2-0-sur03.miramar.fl.pompano.comcast.net (69.139.183.46)  10.091 ms
        xe-11-2-0-0-sur03.miramar.fl.pompano.comcast.net (69.139.183.14)  20.572 ms
        xe-11-1-1-0-sur03.miramar.fl.pompano.comcast.net (69.139.183.177)  9.440 ms
     5  te-9-1-ur01.wellington.fl.pompano.comcast.net (68.85.219.25)  16.879 ms  9.370 ms
        xe-1-0-7-0-ar02.stuart.fl.pompano.comcast.net (68.85.219.29)  16.575 ms
     6  be-20214-cr02.miami.fl.ibone.comcast.net (68.86.90.205)  10.963 ms  12.427 ms  11.617 ms
     7  68.86.82.74 (68.86.82.74)  10.475 ms  11.337 ms  9.979 ms
     8  23.30.207.242 (23.30.207.242)  47.521 ms  45.935 ms  47.899 ms
     9  209.85.241.136 (209.85.241.136)  10.958 ms  10.625 ms  10.479 ms
    10  216.239.42.79 (216.239.42.79)  10.616 ms  11.121 ms  10.590 ms
    11  mia07s35-in-f14.1e100.net (216.58.192.110)  17.763 ms  16.857 ms  11.290 ms
traceroute to google.com (216.58.192.110), 64 hops max, 52 byte packets


That's my currently traceroute for Google.  Yours will definitely be different.  Either way, anything in between could be contributing to a dropped packet which is the request timeout error you are seeing.