Your continuous queue drops might, or might not, be a problem. Besides the queue drops, does there appear to be network performance problems across the WAN link, especially intermittent?
The impact of queue drops depends on the type of traffic being dropped (e.g. UDP vs. TCP) and how it's being dropped (e.g. FIFO global tail, FQ tail, RED). With TCP, how packets are dropped also has somewhat different impact depending on what protocol and/or option "flavor" of TCP is being used (e.g. Tahoe, Reno, new-Reno, SACK, Compound TCP). There's also a question of whether you're trying to obtain best link utilization or minimize latency.
In other words, without analysis or what your traffic is and what you're trying to accomplish, one can't really provide a fully correct answer.
If you think you have a performance issue, Paolo's suggestion of using fair-queue (or fair-queue within CBWFQ), if not already active, is a great first step.
Paolo's other suggestion of traffic shaping the "problem PC" could be effective. Or, you could segregate its bandwidth consumption from other traffic using CBWFQ.
