don't use cheap switches under some scenarios

What do you mean by "intense traffic?" Many switches will get
confused if you fill their tables with a large number of different addresses. Is someone maybe spoofing MAC addresses on your net? Or is the switch plugged into a larger switched network where it will see many different MAC addresses on the uplink port?

Also, almost every switch will flood all ports with traffic for
machines that have disappeared recently (disconnected or changed their MAC addresses.) High-end switches have settings to control this problem but it's impossible to avoid some leakage.

Never count on an ethernet switch to provide privacy for traffic
on a single VLAN.

Chuck,

By Intense traffic I mean that the traffic on one path through the
switch is a little more than 10mb/s.

My testing enviroment is an isolated lab environment. I only use
4 ports and the uplink port is not used. Each of the 4 ports is connected to one ethernet card. That is why I concluded that the 10mb/s traffic is intense since for the first 5 minutes the switch is a switch and then becomes a hub.

As I said, I used a little expensive swicth (also auto-sensing
dumb one) and solved the problem. That is why I concluded a very cheap swicth (<$100) may be not good in some scenarios. Of course for household use,
it is definitely a good choice.

Xinwen Fu
P.S. I only intend to provide some information and all my testing is for a rigid academic objective.