Primary suspect is exchange congestion, if you haven't done so already run a
tracert as per the example
with no downloads of any type running when you experience the problem.
If your second hop (bolded in the example) is in the hundreds of millesecs you probably have exchange congestion, results will vary depending on the time of day. Not much the helpdesk can do if the exchange needs upgrading.
Code:
C:\Users\mick>tracert google.co.za
Tracing route to google.co.za [173.194.34.120]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms ipcop2.mickza [192.168.11.254]
[B][SIZE=3] 2 13 ms 19 ms 19 ms 224-140-1.dsl.subscriber.telkomsa.net [105.224.140.1][/SIZE][/B]
3 38 ms 39 ms 39 ms 226-0-6.dsl.subscriber.telkomsa.net [105.226.0.6]
4 41 ms 49 ms 49 ms 226-0-13.dsl.subscriber.telkomsa.net [105.226.0.13]
5 46 ms 39 ms 49 ms wblv-ip-hsll-1-wan.telkom-ipnet.co.za [196.25.39.45]
6 186 ms 189 ms 189 ms lon-ip-hsll-1-gig-7-1-0.telkom-ipnet.co.za [196.43.9.58]
7 176 ms 189 ms 179 ms 196.25.191.146
8 199 ms 189 ms 269 ms 209.85.240.63
9 188 ms 189 ms 189 ms 209.85.253.47
10 188 ms 189 ms 189 ms lhr14s20-in-f24.1e100.net [173.194.34.120]
Trace complete.