Lag spike when i first get to lane

I have no idea what is going on. Whatever lane i go in during the first encounter with the other laner or when i first see the minions i start i get lag spikes. Although this stops after a few seconds (basically when the first 3 melee minions die) it is getting really annoying as i can never rush level 3 and can never walk up to cs the first minions putting me slightly behind. Note we are talking about something like 200 to 500 ms. Really annoying. Btw i don't know if this is broadband or a general bug. Some help possibly