Assuming that you can actually trace the funds from your 401K (separate property) to your joint account, there is a chance that the Court may deny the levy. The problem is that by placing the funds in your joint account, they may have legally changed their character (the funds) from separate property to community property. With your wife on the account, they are thus subject to levy. The burden of proof is now on you to demonstrate that the funds did not change their legal status / character at the time of being placed in the joint account. That is a high burden to overcome.
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It also depends on how the account is titled. If it is "tenancy by the entireties" (a special joint tenancy reserved only for husband and wife), then a creditor of only one spouse should not be able to access the funds that belong to the married couple together. This doesn't mean that it can't happen, because banks make mistakes every day and release funds that should not be released to the wrong parties. I strongly suggest you retain a qualified attorney in your area to help you with this, especially if substantial funds are involved AND with the hearing coming soon. This is not the time to be "penny wise and pound foolish." Good luck!